Digital broadcasting demodulation apparatus with a direction adjustment indicator for the receiving antenna

ABSTRACT

A signal of a desired channel is selected by a tuner from digital broadcasting is received by an antenna. The condition of the radio wave received by the antenna, which is judged from an AGC signal of the signal of the channel selected by the tuner, a Sync signal detected by a synchronization establishment unit and the number of errors which have not been corrected by a forward error corrector  10 , is displayed on an indicator. The receiving direction or position of the antenna can be easily decided on the basis of the condition of the received radio wave of the antenna, which is displayed on the indicator, so that received video has a C/N within thresholds.

TECHNICAL FIELD

The present invention relates to a digital broadcasting demodulationapparatus which demodulates digital data of digital broadcasting whichare received by an antenna.

BACKGROUND ART

In recent television broadcasting, services using satellites or CATV(Cable Television) have been performed with digital compressiontechnology, digital modulation/demodulation technology and the like.Video is coded according to MPEG 2 (Motion Picture Experts Group 2). Asa digital modulation scheme, a QPSK (Quadrature Phase Shift Keying)scheme is adopted in satellite broadcasting and a QAM (QuadratureAmplitude Modulation) scheme is adopted in CATV. In the US, the groundwave digital broadcasting (DTV) was started in the Autumn of 1998, andvideo compression using MPEG 2 is executed and services are performed ina digital modulation 8VSB (Vestigial Side Bands) scheme.

At present, in ordinary households in the US, loop-type or dipole-typesimple indoor antennas are generally used in receiving the NTSC(National Television System Committee) analog ground wave broadcasting,and relatively good video can be viewed on television. It is alsoexpected that the digital ground wave broadcasting will be received withthe simple indoor antennas in many households. Hereinafter, an exampleof the digital ground wave broadcasting receiving apparatus is describedwith reference to the drawings.

FIG. 6 is a block diagram illustrating a structure of a conventionaldigital broadcasting demodulation apparatus.

The conventional ground digital broadcasting demodulation apparatus 1000comprises a tuner 302 for selecting a signal of a channel from a RFsignal which is received by a loop-type or dipole-type indoor antenna 1,a SAW (Surface Acoustic Wave) filter 303 for subjecting the selectedmodulated signal to the band limitation, an AMP 304 for amplifying thesignal, an orthogonal detector 305 for executing orthogonal detection tothe amplified signal using a-mixer, a first low-pass-filter(hereinafter, referred to as LPF) 306, an A/D converter 307 forconverting an analog signal into a digital signal, a synchronizationestablishment unit 308 for reproducing a clock and detecting a Syncsignal of packet data, a waveform equalizer 309, a forward errorcorrector 311, a data output terminal 311, an AGC (Automatic GainControl) signal detector 312, a second LPF 313, and a Voltage ControlOscillator (hereinafter, referred to as VCO) 321.

The operation of the so-constructed conventional digital broadcastingdemodulation apparatus is described.

The broadcasting station compresses coded digital video data and audiodata, multiplexes the compressed data with various types of information,converts the data into data in a packet format (hereinafter, referred toas packet data), subjects the packet data to RF modulation, andtransmits the data to viewers.

The viewer manually changes the direction of the simple indoor antenna 1so as to obtain a received power having a good C/N (Carrier to NoiseRatio). The antenna 1 receives the RF demodulated signals and transmitsthe signals to the tuner 302 of the digital broadcasting modulationapparatus.

The tuner 302 selects a signal of a channel which is selected by theviewer from the RF modulated signals, subjects the selected signal togain control, and outputs an intermediate frequency (IF) signal.

The SAW filter 303 imposes band limitation on the IF signal which isoutput by the tuner 302 so as to obtain a predetermined frequencycharacteristics, and outputs the signal to the AMP 304.

The AMP 304 receives a control signal from the AGC signal detector 312(which is described later), amplifies the signal which is transmitted bythe SAW filter 303, and outputs the amplified signal to the orthogonaldetector 305.

The orthogonal detector 305 subjects the signal which is output by theAMP 304 to orthogonal detection, and obtains a baseband signal.

The first LPF 306 removes excess higher harmonic components of thebaseband signal. The baseband signal whose higher harmonic componentsare removed is transmitted to the A/D converter 307 and the AGC signaldetector 312.

The AGC signal detector 312 detects an envelope of the baseband signal.

The envelope which is detected by the AGC signal detector 312 istransmitted to the AMP 304 via the second LPF 313 as the AGC signal andthe amplitude of the received modulated signal is controlled by the AMP304. In addition, the AGC signal is supplied by the AMP 304 to the tuner302 to control the operation of the tuner 302. That is, the AGC signalexecutes feedback control for both of the tuner 302 and the AMP 304.

On the other hand, the baseband signal which is input to the A/Dconverter 307 is converted in a digital signal and supplied to thesynchronization establishment unit 308.

The synchronization establishment unit 308 extracts a clock reproductioncontrol signal from the baseband signal and outputs the clockreproduction control signal to the VCO 321 while detecting a Sync signalof the packet data and outputting the packet data to the waveformequalizer 309.

The waveform equalizer 309 controls frequency characteristics of thedata, removes distortion of the data occurring due to interference suchas ghost or multi-path, and outputs the data to the Forward ErrorCorrector (FEC) 310.

The Forward Error Corrector 310 corrects errors in the packet data whichare output from the waveform equalizer 309, and outputs the correcteddata to the output terminal 311 as MPEG transport data. The transportdata which are output from the output terminal 311 are subjected todecoding processing by a decoder (not shown), and video data aredisplayed on a predetermined monitor (not shown) and audio data areoutput from a predetermined audio output unit (not shown).

The VCO 321 feeds back an oscillated frequency signal in accordance withthe clock reproduction signal to the A/D converter 307. Here, the signalwhich is fed back to the A/D converter 307 is generated by a PLL.

However, changes in the image quality of video of the digital groundwave broadcasting are steeper near thresholds of C/N which indicateswhether the video display is sufficiently possible or not, as comparedwith changes in the image quality of video of the analog ground wavebroadcasting such as NTSC. That is, in the digital broadcasting, whenthe C/N is within the thresholds, video having certain image quality canbe displayed under all conditions of a received radio wave. However,when the C/N is outside the thresholds even slightly, the video isinterrupted or frozen.

When the digital ground wave broadcasting is received using theloop-type or dipole-type simple indoor antenna, the direction of theantenna is changed manually, thereby finding an optimum value of thedirectivity or receiving sensitivity. At this time, it is required thatthe received radio wave is displayed on a monitor as video when manuallymoving the antenna and that the image quality of video on the monitor isjudged every time the antenna is moved. However, it is very complicatedto manually decide the receiving direction or position of the antenna,and it is difficult to decide the optimum direction and position of theantenna.

DISCLOSURE OF THE INVENTION

To solve the above-mentioned problems, a digital broadcastingdemodulation apparatus which demodulates signals of digital broadcastingreceived by an antenna, comprises a signal demodulation unit fordemodulating a signal of a desired channel from the digitalbroadcasting; and an indication unit for indicating a parameter which isaffected by a condition of a radio wave received by the antenna amongparameters associated with processing of the signal demodulation unit,to viewers.

According to the digital broadcasting demodulation apparatus of thepresent invention, even when video is not displayed on a monitor duringreception of the broadcasting with a simple indoor antenna or the like,the parameter which is affected by the condition of the radio wavereceived by the antenna is indicated to the viewers by the indicationunit. Therefore, the optimum angle or position of the antenna such thatreceived video has a C/N within the thresholds can be easily found.

In the digital broadcasting demodulation apparatus according to thepresent invention, the signal demodulation unit comprises a tuner forselecting the signal of the desired channel; an AMP for amplifying thesignal selected by the tuner; an orthogonal detector for executingorthogonal detection to the signal amplified by the AMP, to obtain abaseband signal; and an A/D converter for converting the baseband signalinto a digital signal; a synchronization establishment unit fordetecting a Sync signal from the baseband signal which has beenconverted into the digital signal, and generating a Sync signaldetection flag and a digital processing AGC signal for controllingoperations of the AMP and the tuner when the Sync signal is detected.The signal demodulation unit also includes a waveform equalizer forremoving a distortion of the signal which is synchronized by thesynchronization establishment unit; a forward error corrector forcorrecting errors in data which is output by the waveform equalizer; anAGC signal detector for detecting an analog processing AGC signal forcontrolling the operations of the AMP and the tuner from the basebandsignal before being converted into the digital signal; and a switchoutputting the analog processing AGC signal as an AGC signal until theSync signal detection flag is detected, and outputting the digitalprocessing AGC signal as the AGC signal when the Sync signal detectionflag is detected, and the parameter which is affected by the conditionof the radio wave received by the antenna includes at least one of theSync signal detection flag, the AGC signal, a number of errors whichhave not been corrected by the forward error corrector, and the errorwhich is detected by the waveform equalizer.

According to the digital broadcasting demodulation apparatus of thepresent invention, the indication unit is a monitor for indicating avideo signal of the digital broadcasting.

According to the digital broadcasting demodulation apparatus of thepresent invention, even when the video is not displayed on the monitorduring the reception of the broadcasting with the simple indoor antennaor the like, the parameter which is affected by the condition of theradio wave received by the antenna is indicated by the monitor to theviewers. Therefore, the optimum angle or position of the antenna suchthat the received video has a C/N within the thresholds can be easilyfound.

In the digital broadcasting demodulation apparatus of the presentinvention, a judgement unit for comparing the parameter which isaffected by the condition of a radio wave received by the antenna with apreviously set reference, and judging the condition of the radio wavereceived by the antenna is further included, and the indication unitindicates the condition of the received radio wave which is judged bythe judgement unit.

According to the digital broadcasting demodulation apparatus of thepresent invention, even when the video is not displayed on the monitorduring the reception of the broadcasting with the simple indoor antennaor the like, the received radio wave condition which is judged by thejudgement unit is displayed to the viewers by the indication unit.Therefore, the optimum angle or position of the antenna such that thereceived video has a C/N within the thresholds can be easily found.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a structure of a digitalbroadcasting demodulation apparatus according to a first embodiment ofthe present invention.

FIG. 2 is a block diagram illustrating a structure of an orthogonaldetector.

FIG. 3 is a block diagram illustrating a structure of a digitalbroadcasting demodulation apparatus according to a second embodiment ofthe present invention.

FIG. 4 is a block diagram illustrating a structure of a waveformequalizer.

FIG. 5 is a block diagram illustrating a structure CL a digitalbroadcasting demodulation apparatus according to a third embodiment ofthe present invention.

FIG. 6 is a block diagram illustrating a structure of a conventionalground digital broadcasting demodulation apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, digital broadcasting demodulation apparatuses according toembodiments of the present invention will be described with reference tothe attached drawings, taking VSB ground digital broadcasting as anexample.

Embodiment 1.

A digital broadcasting demodulation apparatus according to a firstembodiment of the present invention comprises a signal demodulation unitfor demodulating a signal of a desired channel from digital broadcastingwhich is received by an antenna and outputting the signal to a decoder,and an indication unit, i.e., an indicator for indicating parameterswhich are affected by the received radio wave condition of the antennaamong parameters associated with the processing of the signaldemodulation unit, to a viewer.

As the parameters which are affected by the received radio wavecondition of the antenna, a synchronization detection flag which isdetected by a signal demodulation unit (described later), an AGC signaland the counted number of packet error flags are employed.

FIG. 1 is a block diagram illustrating a structure of a digitalbroadcasting demodulation apparatus 50 according to the firstembodiment. Here, in order to simplify the description, the descriptionis given taking the digital ground wave broadcasting VSB modulationscheme as an example.

The digital broadcasting demodulation apparatus 50 comprises a signaldemodulation unit 51 for demodulating RF modulated signals of digitalbroadcasting which are received by a simple indoor antenna (for example,loop-type or dipole-type antenna) 1, an MPU (Micro Processing Unit) 16and an indicator 17.

The signal demodulation unit 51 comprises a tuner 2 for selecting asignal of a channel from the RF modulated signals which are received bythe antenna 1, a SAW filter 3 for subjecting the selected modulatedsignal to band limitation, an AMP 4 for amplifying the signal, anorthogonal detector 5 for executing orthogonal detection using a mixer,a first LPF 6, an A/D converter 7 for converting an analog signal to adigital signal, a synchronization establishment unit 8, a waveformequalizer 9, a Forward Error Corrector 10, an output terminal 11 foroutputting data to a decoder (not shown), an AGC signal detector 12, aswitch 13, a second LPF 14, a packet error counter 15 for counting thenumber of errors in each packet, and a VCO 21.

The operation of the so-constructed digital broadcasting demodulationapparatus 50 is described.

The tuner 2 selects a signal of a specific channel which is selected bythe viewer from signals of plural channels included in the RF modulatedsignals, adjusts gain of the selected signal in accordance with an AGCsignal (described later), and outputs an intermediate frequency (IF)signal.

The SAW filter 3 imposes the band limitation to predetermined frequencycharacteristics of the IF signal which is output by the tuner 2 andoutputs the signal to the AMP 4.

The AMP 4 amplifies the signal in accordance with the AGC signal andoutputs the signal to the orthogonal detector 5.

The orthogonal detector 5 executes the orthogonal detection to thesignal which is output by the AMP 4 and obtains a baseband signal. Thestructure of the orthogonal detector 5 is described later.

The first LPF 6 removes excess higher harmonic components of thebaseband signal.

The baseband signal whose higher harmonic components are removed istransmitted to the A/D converter 7 and the AGC signal detector 12.

The baseband signal which is input to the A/D converter 7 is convertedinto a digital signal and supplied to the synchronization establishmentunit 8.

The synchronization establishment unit 8 extracts a clock reproductioncontrol signal from the baseband signal and outputs the clockreproduction control signal to the VCO 21 while outputting asynchronization detection flag to the switch 13 and the MPU 16 whendetecting a Sync signal of packet data, outputs a digital processing AGCsignal which is constituted by a known level of the Sync signal to theswitch 13, and outputs data in which the Sync signal is detected to thewaveform equalizer 9.

The waveform equalizer 9 controls the frequency characteristics of thedata, removes the distortion of the data due to the interference such asghost or multi-path, and outputs the data to the Forward Error Corrector(FEC) 10.

The Forward Error Corrector 10 corrects errors in the packet data whichare output from the waveform equalizer 9, outputs a packet error flag toa packet error counter 15 for a packet which cannot have been corrected,and outputs data whose errors have been corrected to the output terminal11 as MPEG transport data. The data which are output by the ForwardError Corrector 10 are decoded by a MPEG decoder (not shown) and outputto a reproduction means for reproducing the digital broadcasting, forexample, a monitor (not shown) for reproducing video data or a speakerfor reproducing audio signals.

The AGC signal detector 12 detects an envelope of the analog basebandsignal, and outputs the detected signal to the switch 13 as an analogprocessing AGC signal.

The switch 13 outputs the analog processing AGC signal or the digitalprocessing AGC signal as the AGC signal in accordance with the Syncsignal detection flag.

The signal output by the switch 13 is transmitted to the AMP 4 and theMPU 16 via the second LPF 14.

The AGC signal controls the amplitude of the received modulated signalin the AMP 4. In addition, the AGC signal is supplied to the tuner 2from the AMP 4, and controls the operation of the tuner 2.

That is, the AGC signal executes the feedback operation for both of thetuner 2 and the AMP 4.

The packet error counter 15 counts the number of packet error flags, andoutputs the counted number to the MPU 16.

The VCO 21 feeds back an oscillated frequency signal on the basis of aclock reproduction signal to the A/D converter 7. Here, the signal whichis fed back to the A/D converter 7 is generated by a PLL.

The MPU 16 controls the whole operation of the signal demodulation unit51. The MPU 16 receives the Sync signal detection flag from thesynchronization establishment unit 8, receives the AGC signal from thesecond LPF 14, and receives the number of packet error flags from thepacket error counter 15. Here, the number of packet error flagsindicates the number of packet data which cannot have been corrected bythe Forward Error Corrector 10. The Sync signal detection flag indicateswhether the Sync signal of the packet data has been detected or not.Therefore, both of the signals are the parameters for estimating thecondition of the radio wave received by the antenna 1. In addition, theAGC signal is a signal for controlling the amplitude level of thereceived radio wave and thus this signal is a parameter indicating thepower of the radio wave received by the antenna 1. Therefore, when theparameters of the counted number of packet error flags, the Sync signaldetection flag and the AGC signal are displayed on the indicator 17, theviewer can easily recognize the condition of the radio wave received bythe antenna 1.

In addition, when references for parameters indicating the processingcondition in the signal demodulation unit 51 are previously set, the MPU16 can operate as a judgement unit for comparing the actual values ofthe parameters with the references and judging the received radio wavecondition of the signal received by the antenna 1, for example the levelof the C/N of the radio wave. At this time, the indicator 17 indicatesthe received radio wave condition which is judged by the MPU 16.

FIG. 2 is a block diagram illustrating a structure of the orthogonaldetector 5.

The orthogonal detector 5 comprises a first mixer 100 for multiplyingthe IF modulated signal which is output by the AMP 4 and an IF signalwhich is output by a local signal oscillator (Lo) 103 (described later)together, a second mixer 101 for multiplying the IF modulated signalwhich is output by the AMP 4 and an output signal of a 90-degree phaseshifter 104 (described later) together, a LPF 102 for removing high-bandcomponents of the output of the second mixer 101, an Lo 103 whichoscillates a local signal from the output of the LPF 102, the 90-degreephase shifter 104 for shifting the phase of the output of the Lo 103 by90 degrees, an input terminal 105 for receiving the signal from the AMP4, and an output terminal 106 for outputting a signal which ismultiplied by the first mixer 100 as a baseband signal.

The second mixer 101 multiplies the IF modulated signal from the AMP 4and the local signal whose phase is shifted by 90 degrees together, andoutputs error components of the obtained signal from a carrier (pilotsignal in the case of the VSB digital ground wave broadcasting)frequency. The error components which are output by the second mixer 101are subjected to the frequency limitation by the LPF 102 and output bythe Lo 103 as the local signal to the first mixer 100 and the 90-degreephase shifter 104.

The operation of oscillating the local signal by the Lo 103 is underfeedback control by the second mixer 101, the LPF 102 and the 90-degreephase shifter 104. Therefore, the Lo 103 can generate the local signalwhich is in phase with the carrier of the IF modulated signal.Accordingly, the orthogonal detection can be executed correctly.

As described above, according to the first embodiment, the angle orposition of the simple indoor antenna can be changed by referring to thereceived radio wave condition of the antenna, which is displayed on theindicator 17. Thereby, the reception power having a good C/N can beeasily obtained. Further, the reception condition of the antenna can bejudged objectively using the Sync signal detection flag, the countednumber of packet errors and the AGC signal, not judging the conditionfrom the video which is displayed on the monitor as in the prior art.

Embodiment 2.

A digital broadcasting demodulation apparatus according to a secondembodiment of the present invention can judge the received radio wavecondition of the signal which is received by the antenna, on the basisof the Sync signal detection flag, the AGC signal and an error which isdetected by the waveform equalizer.

FIG. 3 is a block diagram illustrating a structure of a digitalbroadcasting demodulation apparatus 60 according to the secondembodiment. The same reference numerals as those in the digitalbroadcasting demodulation apparatus 50 of the first embodiment denotethe same or corresponding parts. The descriptions of these parts are notgiven here.

The digital broadcasting demodulation apparatus 60 comprises a signaldemodulation unit 61 for demodulating RF modulated signals of digitalbroadcasting which are received by a simple indoor antenna (for example,loop-type or dipole-type antenna) 1, a MPU (Micro Processing Unit) 16,and an indicator 17.

The signal demodulation unit 61 comprises a tuner 2 for selecting asignal of a channel from the RF modulated signals which are received bythe simple indoor antenna 1, a SAW filter 3 for subjecting the selectedmodulated signal to the band limitation, an AMP 4 for amplifier thesignal, an orthogonal detector 5 using a mixer, a first LPF 6, an A/Dconverter 7 for converting an analog signal into a digital signal, asynchronization establishment unit 8, a waveform equalizer 62, a ForwardError Corrector 63 for correcting errors in packet data which are outputfrom the waveform equalizer 62, a data output terminal 11 for outputtingdata which are output from the Forward Error Corrector 63 as MPEGtransport data, an AGC signal detector 12, a second LPF 14, a switch 13,and a VCO 21.

FIG. 4 is a block diagram illustrating a structure of the waveformequalizer 62.

The waveform equalizer 62 comprises a forward transversal filter(hereinafter, referred to as forward filter) 200, an adder 201, a slicer202 for judging a value of data, a feedback transversal filter(hereinafter, referred to as feedback filter) 203, a filter coefficientoperation unit 205 for calculating coefficients of each of the filtersfrom an error which is detected by an error detector 204 (describedlater), and the error detector 204 for detecting a waveform equalizationerror ε.

The description is given of the so-constructed waveform equalizer 62.

The data which are output by the synchronization establishment unit 8are input to the forward filter 200 to be subjected to frequencycontrol, and then output to the adder 201.

The adder 201 subtracts the output data of the feedback filter 203 fromthe output data of the forward filter 200, then outputs the obtainedresult to the slicer 202, and further outputs the result to the ForwardError Corrector 10 as the output data of the waveform equalizer 62.

The slicer 202 compares the data value of the input data with anarbitrary reference value to obtain a signal of a predetermined level,and outputs the signal to the feedback filter 203.

The feedback filter 203 executes the frequency control for the inputsignal, and outputs the signal to the adder 201.

Therefore, the signal output from the adder 201 makes a round of theslicer 202 and the feedback filter 203, and the frequency control forthe output signal of the forward filter 200 is executed in the adder201.

On the other hand, the error detector 204 correlates the output data ofthe adder 201 and the input data of the waveform equalizer 62 to eachother, and detects the waveform equalization error ε. The detected errorε is output to the filter coefficient operation unit 205 and the MPU 16.

The filter coefficient operation unit 205 calculates the coefficients ofthe forward filter 200 and the feedback filter 203 from the error ε, andupdates the coefficients of the filters.

The MPU 16 receives the Sync signal detection flag from thesynchronization establishment unit 8, receives the AGC signal from thesecond LPF 14, and receives the waveform equalization error ε from thewaveform equalizer 62. Here, the Sync signal detection flag indicateswhether the Sync signal of the packet data has been detected or not.Accordingly, this flag is used as an index for showing the condition ofthe radio wave which is received by the antenna. The AGC signal is asignal for controlling the amplitude level of the received radio wave.Accordingly, the AGC signal is used as an index for showing the power ofthe received radio wave. In addition, when the received radio wave isaffected by ghost, multi-path or the like, the waveform equalizationerror ε grows larger. On the other hand, when the received radio wave isnot affected by the interference or the like and the reception conditionis good, the error ε grows smaller. Therefore, the condition of theradio wave received by the antenna can be recognized from the Syncsignal detection flag, the AGC signal and the waveform equalizationerror ε. Accordingly, when the above parameters are displayed on theindicator 17, the viewer can be easily informed of the received wavecondition of the antenna 1.

Here, similar to the first embodiment, it is also possible that the MPU16 compares the values of the actually detected parameters with thepreviously set references to judge the received radio wave condition ofthe antenna 1, and the indicator 17 indicates the judgement result.

As described above, according to the second embodiment, the viewer canchange the angle or position of the simple indoor antenna by referringto the received radio wave condition of the antenna, which is displayedon the indicator 17. Therefore, the reception power having a good C/Ncan be easily obtained. In addition, the reception condition of theantenna can be objectively judged using the Sync signal detection flag,the AGC signal and the waveform equalization error ε, not using thevideo which is displayed on the monitor as in the prior art.

Embodiment 3.

While in the digital broadcasting demodulation apparatus according tothe first and second embodiments the condition of the received radiowave of the antenna is displayed on the indicator 17, a digitalbroadcasting demodulation apparatus according to a third embodiment isfurther provided with an OSD signal generation circuit to display thereceived radio wave condition of the antenna on a monitor which is ameans for displaying video data of the digital broadcasting.

FIG. 5 is a block diagram illustrating a structure of a digitalbroadcasting demodulation apparatus 70 according to the thirdembodiment. The same reference numerals as those of the digitalbroadcasting demodulation apparatus 50 according to the first embodimentand the digital broadcasting demodulation apparatus 60 according to thesecond embodiment denote the same or corresponding parts, and thedescriptions thereof are not given here. In the digital broadcastingdemodulation apparatus 70 as shown in FIG. 5, the Sync signal detectionflag, the AGC signal and the waveform equalization error ε are used asthe parameters for judging the received radio wave condition of theantenna as in the second embodiment. However, as in the firstembodiment, the Sync signal detection flag, the counted number of packeterrors and the AGC signal can be used.

Hereinafter, the operation of the digital broadcasting demodulationapparatus is described with reference to the drawings.

According to the digital broadcasting demodulation apparatus 70 as shownin FIG. 5, a digital broadcasting monitor 20 has the function of theindicator 17 of the digital broadcasting demodulation apparatus 60according to the second embodiment as shown in FIG. 3, and the digitalbroadcasting demodulation apparatus further comprises an OSD (On ScreenDisplay) signal generation circuit 18.

The MPU 16 outputs the packet Sync signal detection flag, the AGC signaland the waveform equalization error ε to the OSD signal generationcircuit 18 as in the second embodiment. Alternatively the MPU 16 judgesthe condition of the radio wave received by the antenna 1 on the basisof the packet Sync signal detection flag, the AGC signal and thewaveform equalization error ε, and outputs the judgement result to theOSD signal generation circuit 18.

The OSD signal generation circuit 18 generates an image for informingthe viewer of the condition of the received radio wave. At this time,the OSD signal generation circuit 18 composes the Sync signal of videodata which are detected by the synchronization establishment unit 8 withan image to be displayed on the monitor 20, and outputs a composed imageto the monitor 20. For example, the OSD signal generation circuit 18 cangenerate an image for displaying the values of the parameters which arereceived by the MPU 16. In addition, it is also possible that the MPU 16compares the parameters with previously set references to calculate alevel value of the C/N, and the OSD signal generation circuit 18generates an image for showing the level value of the C/N. Here, whetherthe received radio wave condition is to be displayed on the monitor 20or not can be selected by the viewer.

As described above, the condition of the received radio wave isdisplayed on the monitor 20 in parallel with video data, without using adecoded signal of the video data, whereby the viewer can be easilyinformed of the received radio wave condition of the antenna. Further,even when the received radio wave condition of the antenna is too bad todecode data of the digital broadcasting, the received radio wavecondition can be displayed on the monitor 20. Therefore, the viewer caneasily find a point where the received radio wave condition is the best,by changing the angle or position of the antenna 1, on the basis of thereceived radio wave condition which is displayed on the monitor 20.

In the first to third embodiments, the combination of the Sync signaldetection flag, the counted number of the packet errors and the AGCsignal, or the packet Sync signal detection flag, the AGC signal and thewaveform equalization error ε is used as the reference for the MPU 16 tojudge the condition of the radio wave received by the antenna 1.However, at least one of the Sync signal detection flag, the countednumber of the packet errors, the AGC signal and the waveformequalization error ε can be selected as the judgement reference. Inaddition, signals other than the above signals, which are detected inthe signal demodulation unit 51 or 61 and affected by the receptioncondition of the antenna 1, can be used as the judgement references.

Further, in the first to third embodiments, the descriptions are giventaking the digital ground wave broadcasting VSB modulation scheme as theexample. However, the scheme of the digital broadcasting is notrestricted to the digital ground wave broadcasting VSB modulationscheme.

The digital broadcasting demodulation apparatus according to the presentinvention comprises a signal demodulation unit for demodulating a signalof a desired channel from digital broadcasting, and an indication unitfor indicating to viewers parameters which are affected by the conditionof the radio wave received by the antenna among parameters associatedwith processing of the signal demodulation unit. Thereby, when theground digital broadcasting is received using a simple indoor antenna orthe like, the optimal angle or position of the antenna can be easilyfound objectively by referring to the received radio wave condition ofthe antenna which is displayed on the indication unit, withoutdisplaying video on the monitor. Accordingly, it is useful particularlywhen the optimal value of the directivity or reception sensitivity ofthe antenna is to be found by manually changing the direction of theantenna.

What is claimed is:
 1. A digital broadcasting demodulation apparatuswhich demodulates signals of digital broadcasting received by anantenna, comprising: a signal demodulation unit operable to demodulate asignal of a desired channel from the digital broadcasting; and anindication unit operable to display a parameter which is affected by acondition of a radio wave received by the antenna among parametersassociated with processing of the signal demodulation unit, to viewers,wherein said signal demodulation unit comprises: a tuner operable toselect the signal of the desired channel; an AMP operable to amplify thesignal selected by the tuner; an orthogonal detector operable to executeorthogonal detection to the signal amplified by the AMP, to obtain abaseband signal; an A/D converter operable to convert the basebandsignal into a digital signal; a synchronization establishment unitoperable to detect a Sync signal from the baseband signal which has beenconverted into the digital signal, and generate a Sync signal detectionflag and a digital processing AGC signal for controlling operations ofthe AMP and the tuner when the Sync signal is detected; a waveformequalizer operable to remove a distortion of data which is synchronizedby the synchronization establishment unit; a forward error correctoroperable to correct errors in data which are output by the waveformequalizer; an AGC signal detector operable to detect an analogprocessing AGC signal for controlling the operations of the AMP and thetuner from the baseband signal before being converted into the digitalsignal; and a switch operable to output the analogs processing AGCsignal as an AGC signal until the Sync signal detection flag isdetected, and output the digital processing AGC signal as the AGC signalwhen the Sync signal detection flag is detected, wherein the parameterwhich is affected by the condition of the radio wave received by theantenna includes at least one of the Sync signal detection flag, the AGCsignal, a number of errors which have not been corrected by the forwarderror corrector, and an error which is detected by the waveformequalizer.
 2. The digital broadcasting demodulation apparatus of claim 1wherein the indication unit is a monitor operable to display a videosignal of the digital broadcasting.
 3. The digital broadcastingdemodulation apparatus of claim 1, further comprising: a judgement unitoperable to compare the parameter which is affected by the condition ofthe radio wave received by the antenna with a previously set reference,and judge the condition of the radio wave received by the antenna,wherein the indication unit indicates the condition of the receivedradio wave which is judged by the judgement unit.
 4. The digitalbroadcasting demodulation apparatus of claim 2, further comprising: ajudgement unit operable to compare the parameter which is affected bythe condition of the radio wave received by the antenna with apreviously set reference, and judge the condition of the radio wavereceived by the antenna, wherein the indication unit indicates thecondition of the received radio wave which is judged by the judgementunit.